Set all channels to Pre/Post

How do you set all channels to PRE or POST for 1 mix in Director?
I’ve tried right-clicking and other shortcuts, but I can’t seem to figure out how to do this.

select the MIX button at the Mix Master strip
then you have under the display two buttons
left one is PRE/POST, right one is ON/OFF

Aha! Very tricky.

Thank you!